Tropical deforestation appears to have larger impacts on local, regional and global climate when it occurs under maritime
conditions rather then under continental conditions.
At the local scale, we compare results from a field experiment in Puerto Rico with other long-term studies of the changes in
surface fluxes after deforestation. Changes in surface fluxes are larger in maritime situations because a number of feedback
mechanisms appears less relevant (e.g. the dependency of soil moisture on recycling of water and the larger reduction of net
radiation in the wet season due to clouds in continental regions). Pastures may evaporate at similarly high rates as forests when soil
moisture is sufficient, which has a strong reducing effect on the sensible heat flux after deforestation.
At the regional scale (∼102 km2), model simulations show that the meso-scale sea breeze circulation under maritime conditions
is more effective in transporting heat and moisture to the upper troposphere than convection is in the continental case. Thus islands
function as triggers of convection, whereas the intensity of the sea breeze-trigger is sensitive to land use change.
At the global scale, using satellite-derived latent heating rates of the upper troposphere, it is shown that 40% of the latent
heating associated with deep convection takes place in the Maritime Continent (Indonesia and surroundings) and may be produced
mostly by small islands. Continents contribute only 20% of the latent heating of the upper troposphere. Thus, sea breeze
circulations exert significant influence on the Hadley cell circulation. These results imply that, from a climate perspective, further
deforestation studies would do well to focus more on maritime conditions.

PowerPoint:
Watershed protection as an ecosystem service?
“Forests are assumed to be economically important for preventing soil erosion and flooding, protecting the water supply, and maintaining rainfall patterns. These assertion are often made with little supporting evidence.…First, benefits must be computed relative to an alternative land use. Second, benefit levels are highly location-specific and scale dependent”.

A climatological analysis of the differences of air temperature between rural and urban areas (dT(U–R)) corroborates
the existence of an urban heat island (UHI) in the tropical coastal city of San Juan, Puerto Rico that has been increasing at
a rate of 0.06 1Cyear1 for the last 40 years with predicted differences as high as 8 1C for the year 2050. The Regional
Atmospheric Model System (RAMS) was used to validate the presence of this UHI and to simulate and compare three
different land use scenarios consisting of potential natural vegetation, present, and projected future to quantify the impact
of the urban development in the regional climate of Puerto Rico. RAMS simulated the UHI conditions at the lower and
upper atmosphere revealing significant changes in sensible heat fluxes and sinks, and an increasing low turbulent-kineticenergy
zone (LTKEZ) over the urbanized area of San Juan.

The Hydrometeorological Design Studies Center (HDSC), Hydrology Laboratory,
Office of Hydrologic Development, U.S. National Weather Service is updating its
precipitation frequency analysis for Puerto Rico and the Virgin Islands. Current
precipitation frequency studies for the area are contained in Technical Paper No. 42
"Generalized estimates of probable maximum precipitation and rainfall-frequency data
for Puerto Rico and Virgin Islands" (U.S. Weather Bureau 1961) and Technical Paper
No. 53 "Two- to ten-day rainfall for return periods of 2 to 100 years in Puerto Rico and
Virgin Islands" (Miller 1965). The current study includes collecting data and performing
quality control, compiling and formatting datasets for analyses, selecting applicable
frequency distributions and fitting techniques, analyzing data, mapping and preparing
reports and other documentation.
The study will determine annual and seasonal precipitation frequencies for
durations from 5 minutes to 60 days, for return periods from 2 to 1000 years. The study
will review and process all available rainfall data for the Puerto Rico and Virgin Island
study area and use accepted statistical methods. The study results will be published as
a Volume of NOAA Atlas 14. They will also be made available on the internet using
web pages with the additional ability to download digital files.

Wind data was measured at a number of sites on the Caribbean island of Puerto Rico over
a 24 calendar-month time frame. The wind data gathered at four sites is envisaged to shed
new light on the wind characteristics of this tropical island with an emphasis on the climate’s
suitability for wind energy technology applications. Characteristics such as the diurnal,
monthly and annual wind speed are subjectively investigated to determine the sites’ potential
for further studies in the wind measurement field. Reasonable wind conditions for wind energy
conversion system installation seem to exist in and around Aguadilla and Ponce.

Beautiful and breezy cities on small tropical
islands, it turns out, may not be exempt
from the same local climate change effects
and urban heat island effects seen in large
continental cities such as Los Angeles or
Mexico City. A surprising, recent discovery
indicates that this is the case for San Juan,
Puerto Rico, a relatively affluent coastal tropical
city of about two million inhabitants that
is spreading rapidly into the once-rural areas
around it.
A recent climatological analysis of the surface
temperature of the city has revealed that
the local temperature has been increasing over
the neighboring vegetated areas at a rate of
0.06°C per year for the past 30 years.This is
a trend that may be comparable to climate
changes induced by global warming.
These results encouraged the planning and
execution of an intense field campaign in
February 2004, referred to as the San Juan Atlas
Mission, to verify the spatial and temporal
extent of this urban heat index. Results of this
field campaign recently have been analyzed
and are the main topic of this article.
These results reveal the warming of a tropical
coastal city that is significantly higher than
typical temperatures in vegetated areas.This
may be the first set of high-resolution thermal
images taken in a tropical coastal city. Figure 1
shows that the daytime surface temperatures
of a portion of San Juan at fi ve-meter resolution
are as high as 60°C,and that differences
between urbanized and limited vegetation
areas are in excess of 30°C.

Using results from a factor analysis regionalization of nontropical storm convective rainfall over the island
of Puerto Rico, a statistical methodology is investigated for its potential to forecast rain events over limited
areas. Island regionalization is performed on a 15-yr dataset, while the predictive model is derived from 3 yr
of surface and rainfall data. The work is an initial attempt at improving objective guidance for operational
rainfall forecasting in Puerto Rico. Surface data from two first-order stations are used as input to a partially
adaptive classification tree to predict the occurrence of heavy rain. Results from a case study show that the
methodology has skill above climatology—the leading contender in such cases. The algorithm also achieves
skill over persistence. Comparisons of forecast skill with a linear discriminant analysis suggest that classification
trees are an easier and more natural way to handle this kind of forecast problem. Synthesis of results confirms
the notion that despite the very local nature of tropical convection, synoptic-scale disturbances are responsible
for prepping the environment for rainfall. Generalizations of the findings and a discussion of a more realistic
forecast setting in which to apply the technology for improving tropical rainfall forecasts are given.

ABSTRACT.—Relatively large, topographically complex tropical islands can produce diurnal precipitation
patterns that vary considerably over relatively short distances. In this investigation, we assembled a variety
of databases to analyze diurnal rainfall patterns in Puerto Rico. We found strong diurnal cycles for all parts
of the island with times of maximum frequency or total that ranged from pre-dawn in the east to midafternoon
in the west. The pattern is similar to findings from Hawaii, and appears related to the daily pattern
of katabatic and anabatic winds interaction with the predominant easterly trade winds. The diurnal pattern
in rainfall was consistent through the year and not significantly affected by local sea-surface temperatures,
El Niño-Southern Oscillation, and/or the North Atlantic Oscillation.

The variability of the insect-borne disease dengue in Puerto Rico was studied in relation
to climatic variables in the period 1979–2005. Annual and monthly reported dengue
cases were compared with precipitation and temperature data. Results show that the
incidence of dengue in Puerto Rico was relatively constant over time despite global
warming, possibly due to the offsetting effects of declining rainfall, improving health
care and little change in population. Seasonal fluctuations of dengue were driven by
rainfall increases from May to November. Year-to-year variability in dengue cases was
positively related to temperature, but only weakly associated with local rainfall and an
index of El Nin˜ o Southern Oscillation (ENSO). Climatic conditions were mapped with
respect to dengue cases and patterns in high and low years were compared. During
epidemics, a low pressure system east of Florida draws warm humid air over the
northwestern Caribbean. Long-term trends in past observed and future projected
rainfall and temperatures were studied. Rainfall has declined slowly, but temperatures
in the Caribbean are rising with the influence of global warming. Thus, dengue may
increase in the future, and it will be necessary to anticipate dengue epidemics using
climate forecasts, to reduce adverse health impacts.

Annually resolved coral delta O-18 and Sr/Ca records from southwestern Puerto Rico are used to investigate Caribbean climate variability between 1751 and 2004 C. E. Mean surface ocean temperatures in this region have increased steadily by about 2 degrees C since the year 1751, with Sr/Ca data indicating 2.1 +/- 0.8 degrees C and delta O-18 data indicating 2.7 +/- 0.5 degrees C. Coral geochemical records from across the tropics demonstrate that regional variability is important for understanding climate variations at centennial time scales. A strong multidecadal salinity signal in the oxygen isotope data correlates with observed multidecadal temperature variations in the Northern Hemisphere. Instrumental wind and precipitation data indicate that the most recent coral isotopic variations are caused by expansion and contraction of the steep regional salinity gradient, forced by trade wind anomalies through meridional Ekman transport. The timing of the fluctuations suggests that the multidecadal-scale wind and surface circulation anomalies might play a role in Atlantic temperature variability and meridional overturning circulation, but further work is needed to confirm this suggestion.